A known machine tool (SE 418 259) has a turbine rotor with turbine blades provided at the periphery. Each pair of blades forms together with the adjacent inner wall of the turbine housing a chamber which is open at two axially opposed sides of the rotor. Especially the spent and expanded medium which leaves the chamber at the side opposite to the outlet opening of the housing contacts the stationary part of the housing and interferes with the fresh medium entering the chamber during the next revolution of the turbine rotor. A disadvantage resulting from the constant interference between spent and fresh medium is the weak "braked power" ability of the machine tool when working in various sorts of material and under increasing or varying load conditions. With this ability is meant that the machine tool should keep a constant speed despite any variations in load.
Another known machine tool (GB No. 547 777) has a disc-shaped turbine rotor with discrete recesses in the periphery which are spaced apart in circumferential direction. From the bottom of each recess a radial bore leads to radial inwardly provided axial outlet channels. Additionally an inclined bore begins in the front or actuation wall of each recess and leads into the radial bore of the next following recess. Interferences between fresh supplied medium and the spent and expanded medium cannot be avoided and a certain part of the jet energy is wasted for the disposal of the medium through the long channels. Furthermore, the manufacture of the rotor is unduly expensive.
U.S. Pat. No. 845,059 describes a jet turbine with a disc-shaped turbine rotor having approximately semi-circular pockets in one side surface separated by partition walls. The pockets and the partition walls are inclined in the jet flow direction. Each pocket consists of three staggered steps of equal length. Each step has one curved front actuation surface. The jet enters the pocket on one side, is deviated along the actuation surface and leaves the pocket at the opposite side where an outlet opening is provided. During its way along the surface the jet produces a reaction force which drives the rotor. The jet only works in one pocket for a very short time period. For the longer time, it is split up and has to actuate two pockets simultaneously. A significant part of the jet energy is necessary to clear the pockets of expanded medium. Nevertheless, a certain amount of expanded medium rests within each pocket and interferes with the next jet dose entering during the next revolution.
Finally, U.S. Pat. No. 848,587 describes a jet turbine having a disc-like rotor with approximately semi-circular pocket shaped recesses in one side of the disc or in the periphery respectively. The pockets are inclined in the jet direction. Each pocket is separated from the adjacent ones by partition walls and consists of one main pocket part and one staggered supplemental pocket part within the main pocket part. Between the parts of the pocket a partition wall is provided which is cut out at the inlet side of the pocket to define a narrow inlet opening to the main pocket part. The jet enters each pocket or pocket part at one side, is then deviated along the semi-circular surfaces and leaves the pocket at the opposite side where outlet openings are provided. The pockets are difficult to manufacture and there cannot be avoided interferences between the jet and the expanded medium as well as between the jet and the partition walls. This known turbine also is a reaction turbine which is driven by deviating the jet.
It is one task of the invention to improve the jet turbine in a machine tool as explained above. Said jet turbine ought to be simple in manufacture and less expensive than the known devices and has an improved efficiency by avoiding significant interferences between the jet and the spent or expanded medium in each recess.
It is furthermore an object of the invention to improve the ability of such a machine tool to keep an essentially constant and high working speed despite variations in load, that means to increase the so-called "braked power" ability of the machine tool.
These objects are achieved with a jet turbine, wherein the inlet nozzle is directed towards the deepest section of the front and concave actuation wall, that each recess is provided with a concave side wall opposite to the outlet opening and also is provided with a concave rear wall opposite to the front actuation wall, that there is provided a flat bottom surrounded by the front actuation wall, the side wall and the rear wall which are interconnected with each other, and that the bottom is inclined downwardly opposite to the flow direction of the jet when the jet initially impacts against the front wall so that said rear, side and bottom walls define an expansion space below the jet with increasing depth towards the rear wall, and also defining a guiding path towards the outlet opening for the expanding jet medium.
Since the jet is directed to the deepest section of the front surface and since additionally the form of the rear wall leads to greater peripheral length of the recess, this allows the jet to actuate the front surface for a long time period and with its direct impact force, each recess works very efficiently. The turbine does work as an action turbine with the impact forces of the jet and not, as it is known from the prior art, as a reaction turbine with jet deviation (i.e. bending). The turbine rotor is simple to manufacture since the configuration of each recess is very simple. The most important advantage of this construction lies in the fact that the jet is not interfered with by the expanding medium since there occurs a pumping effect from the expansion space along the guiding path for the expanding medium. Due to the rotational movement of the recess (in the jet working direction) the medium rebounding from the front wall is forced along the side wall and the rear wall towards the outlet opening, which movement is assisted by a pumping effect which takes place below the jet. In the expansion space near the rear wall, said expansion space having a triangular cross section as seen in the axial direction of the rotor there exists lower pressure than near the front wall, due to the fact that in and near the boundary layer of a medium jet low pressure is produced which in that case helps to suck the expanding medium away from the area of the front wall where the jet impacts. Under the continuous acceleration of the rotor and during and after the working period of the jet in each recess, the mass of caught medium is forced along the guiding path and through the outlet opening. When each recess again passes the inlet nozzle, it is completely emptied and ready for a new working period under the same positive working conditions as before. Since each recess only is open towards the exhaust outlet opening of the housing and the spent medium is disposed very quickly, considerably improved flow conditions have been achieved as compared with the prior art turbines, which directly improves the braked power ability of the machine tool driven by the jet turbine. This is the main reason why the tool machine driven by the jet turbine is so strong that it can keep a high, essentially constant working speed despite increasing or varying load conditions. The efficiency of the medium jet is considerably raised. A machine tool with a jet turbine according to the invention has a run away speed of approximately 80,000 r.p.m. at a medium pressure of 6 bars, whereas the working speed at normal load conditions is kept at approximately 74,000 r.p.m.
Due to the advantageous pressure medium flow conditions, the noise level of the machine tool is extremely low, which of course is important from the working environment point of view.
Advantageous embodiments of the invention are contained in the depending claims.